The invention relates to a method of preventing a wire from becoming entangled in a reinforcing bar fastening machine that judges that a reinforcing bar fastening wire is fastening an object to be fastened such as reinforcing bars and other structures correctly, and that forcibly brings the fastening operation to an end when it is judged that the reinforcing bar fastening wire is not fastening the object correctly.
Generally, in the case where reinforced concrete is employed for constructing buildings and structures, concrete is deposited after crisscrossing reinforcing bars have been fastened. Recently, a reinforcing bar fastening machine is used for fastening reinforcing bars. As shown in FIG. 5, such reinforcing bar fastening machine is operated in the following manner. A main switch 20 is turned on in advance, and a wire 22 is fed by operating a trigger lever 21 at the time of performing a fastening operation. Then, the thus fed wire 22 is further forwarded so as to form a loop from a curved section in the front of a guide arm 23, and such loop of the wire is wound around a crossing point of reinforcing bars 24. Then, part of the wire loop 25 is thereafter picked up with a twisting hook 26 and twisted to thereby fasten the reinforcing bars. The torque of a motor 28 that drives a twisting device 27 for turning the twisting hook 26 is measured, and when the torque of the motor reaches a predetermined value, the reinforcing bar fastening machine judges that the fastening operation has been completed, and therefore stops the operation of the twisting device (the motor 28).
However, when a wire fed from the reinforcing bar fastening machine is not guided regularly into the wire guide while abutted against reinforcing bars or other structures, or when the twisting hook fails to pick up the wire loop even if the wire has been wound around the reinforcing bars or other structures correctly, the twisting device performs the twisting operation with no load. Since there is no load, the torque of the motor does not increase (see FIG. 6). For this reason, the peak of the torque cannot be detected. Therefore, a control means applies a forced stop signal for stopping the motor to thereby forcibly stop the operation of the twisting device upon elapse of a predetermined time set in advance. However, when the twisting device performs the twisting operation for the set time by forwarding the twisting hook with the wire not wound around the reinforcing bars, the wire gets entangled in the twisting hook, which in turn has made the operation of removing the entangled wire extremely cumbersome.